1. Field of the Invention
The invention relates to an improved fuel injection valve for an internal combustion engine, having a valve element whose switched position depends at least indirectly on the switched state of a piezoelectric actuator, which is acted on by a tubular, largely cylindrical prestressing device, which is manufactured out of a plate-shaped starting material and has at least two longitudinal edges that abut each other.
2. Description of the Prior Art
A valve device of the type with which this invention is concerned is known from the market, and is used in fuel injection valves for internal combustion engines with direct injection. Fuel injection valves of this kind are connected to a fuel accumulator (“rail”) in which fuel is stored at high pressure. They each inject the fuel directly into a respective combustion chamber associated with them. Executing an injection requires the triggering of a piezoelectric actuator which either influences a switched position of a valve element of the fuel injection valve directly or triggers a secondary valve that is able to influence the pressure in a hydraulic control chamber of the fuel injection valve. The pressure in the hydraulic control chamber in turn influences the switched position of the valve element.
In valve devices of this type, the use of piezoelectric actuators has proven valuable because they have very short switching times which permit a very precise introduction of the desired quantity of fuel into the combustion chamber. However, piezoelectric actuators are very delicate, mechanically speaking. In order to prevent the piezoelectric actuator from damaging or even destroying itself when executing a length change triggered by an actuation, the piezoelectric actuator is subjected to a compressive force from the very beginning. This usually occurs by means of a tube spring, which is manufactured out of a plate-shaped starting material also referred to as a “blank”. The longitudinal edges abutting each other in the final state can be welded to each other, but this is complex and expensive, not to mention the fact that such welds have a limited service life. It is therefore preferable to use tube springs of this kind in which the longitudinal edges of the plate-shaped starting material abut each other evenly but are not connected to each other in a frictionally engaging manner.
The object of the present invention is to modify a valve device of the type mentioned at the beginning so as to lend it the longest service life possible.
This object is attained in that the prestressing device has at least one region whose longitudinal rigidity differs from that of a neighboring region and is situated in relation to the abutting longitudinal edges so as to reduce the bending moment acting on the piezoelectric actuator, which is generated by the altered longitudinal rigidity in the region of the abutting longitudinal edges.